Heralded for more than a decade, climate change may seem no surprise. But just as some unexpected happening is no surprise while its specific quality is, so it is with climate change. A debate over supersonic airplanes projected cooling to have a dire impact. Observations of rising brought dire projection of warming and drying. When the American breadbasket turned dry in 1988, the warmer, drier climate seemed at hand. But during 1993, floods in the Amer ican heartland discredit or at least discount predictions made only five years before. Computer simulations, of course, had disagreed all along whether rising would make North America drier or wetter. So unsure of what it actually may be, I place climate change among surprises.
In the short run before adaptation, most climate change will lower yields. Even in the long run, if cropland in temperate climates grows hot or dry, yields will fall and land may be taken from Nature for crops. On the other hand, if cropland too cold warms and that too dry moistens, yields will rise, saving other land for Nature. Conflicting and changing projections and experience mean that farmers can only diversify portfolios (Council for Agricultural Science and Technology, 1992[fAST92]) and await the surprises.